Inorganic materials have long been used as fillers, pigments, reinforcements and chemical reactants in polymers. They are essentially hydrophilic, i.e., easily wetted by water or able to adsorb water. However, their compatibility with polymers is limited. Therefore, poor utilization is obtained of the potential reinforcement, of color or opacity, or chemical reactivity of inorganic materials.
For example, zinc oxide is a commonly used component in rubber compounds. When comminuted zinc oxide is added to a rubber compound as a dry powder, it is difficult to disperse it completely in the rubber. On the other hand, predispersion of the zinc oxide in an organic medium which is a plasticizer for the rubber forms a stiff paste which is not dusty, is easy to weigh, and aids in the dispersion in the rubber.
Likewise, other comminuted inorganic solids such as magnesium oxide, calcium oxide, other metal oxides, and fillers such as clay, calcium carbonate, colloidal silica and carbon black may be predispersed in an organic plasticizer or polymer prior to addition to a rubber or plastic compound.
Organo-titanium compounds are well known. A wide variety may be prepared from tetraalkyl ortho titanates by reaction with organic acids.
Organo-titanates having di- or tri- alkyl hydrolyzable groups and with, therefore, only one or two organic groups which are non-hydrolyzable have been used to treat the surfaces of inorganic materials in order to render them hydrophobic, as for example in U.S. Pat. No. 3,660,134. Such di- or tri- alkyl hydrolyzable titanates form a multi-molecular layer or envelope around the inorganic particles, resulting in less efficient use of the organo-titanate, as well as a weaker bond between the inorganic particle surface and the organic continuous phase.
The reaction is accomplished by adding the organo-titanate to a suspension of the inorganic material in an inert solvent such as naphtha, trichloroethylene, toluene or hexane. After the reaction is completed, the solvent is removed and the treated, dried inorganic material is subsequently incorporated in an organic polymer system. U.S. Pat. No. 3,697,475, for example, incorporates such treated inorganic fillers in thermoplastic polymer films.